An AndroidThings button you can use to run something in a 1 liner call

1_use.java

Runnable somethingIWannaDo = new Runnable() {
  @Override
  public void run() {
    Log.d("EZ", "I got ran");  
  }
};

// In Android Activity onCreate:

RunnableButton.create("BCM21", somethingIWannaDo).onCreateInjectInto(this);

RunnableButton.java

import android.app.Activity;
import android.app.Application;
import android.os.Bundle;
import android.util.Log;

import com.google.android.things.pio.Gpio;
import com.google.android.things.pio.GpioCallback;
import com.google.android.things.pio.PeripheralManagerService;

import java.io.IOException;

class RunnableButton {

    private final PeripheralManagerService service;
    private final Runnable runnable;
    private final String buttonPin;

    private Gpio bus;

    static RunnableButton create(String pin, Runnable runnable) {
        return new RunnableButton(new PeripheralManagerService(), pin, runnable);
    }

    private RunnableButton(PeripheralManagerService service, String buttonPin, Runnable runnable) {
        this.service = service;
        this.runnable = runnable;
        this.buttonPin = buttonPin;
    }

    void onCreateInjectInto(final Activity injectedActivity) {
        onCreate();
        final Application application = (Application) injectedActivity.getApplicationContext();
        Application.ActivityLifecycleCallbacks lifecycleCallbacks = new Application.ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                if (theSame(activity, injectedActivity)) {
                    onCreate();
                }
            }

            /**
             * @return true if same activity **assumes** one instance of an Activity i.e. compares activity name
             */
            private boolean theSame(Activity activity1, Activity activity2) {
                return activity1.getClass().getSimpleName().equals(activity2.getClass().getSimpleName());
            }

            @Override
            public void onActivityStarted(Activity activity) {
                if (theSame(activity, injectedActivity)) {
                    onStart();
                }
            }

            @Override
            public void onActivityResumed(Activity activity) {
                // not used
            }

            @Override
            public void onActivityPaused(Activity activity) {
                // not used
            }

            @Override
            public void onActivityStopped(Activity activity) {
                if (theSame(activity, injectedActivity)) {
                    onStop();
                }
            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
                // not used
            }

            @Override
            public void onActivityDestroyed(Activity activity) {
                if (theSame(activity, injectedActivity)) {
                    onDestroy();
                }
                application.unregisterActivityLifecycleCallbacks(this);
            }
        };
        application.registerActivityLifecycleCallbacks(lifecycleCallbacks);
    }

    private void onCreate() {
        try {
            bus = service.openGpio(buttonPin);
        } catch (IOException e) {
            throw new IllegalStateException(buttonPin + " bus cannot be opened.", e);
        }

        try {
            bus.setDirection(Gpio.DIRECTION_IN);
            bus.setActiveType(Gpio.ACTIVE_LOW);
        } catch (IOException e) {
            throw new IllegalStateException(buttonPin + " bus cannot be configured.", e);
        }
    }

    private void onStart() {
        try {
            bus.setEdgeTriggerType(Gpio.EDGE_BOTH);
            bus.registerGpioCallback(touchButtonACallback);
        } catch (IOException e) {
            throw new IllegalStateException(buttonPin + " bus cannot be monitored.", e);
        }
    }

    private final GpioCallback touchButtonACallback = new GpioCallback() {
        @Override
        public boolean onGpioEdge(Gpio gpio) {
            try {
                if (gpio.getValue()) {
                    Log.i("TUT", "ON PRESSED DOWN");
                } else {
                    runnable.run();
                }
            } catch (IOException e) {
                throw new IllegalStateException(buttonPin + " cannot be read.", e);
            }
            return true;
        }
    };

    private void onStop() {
        bus.unregisterGpioCallback(touchButtonACallback);
    }

    private void onDestroy() {
        try {
            bus.close();
        } catch (IOException e) {
            Log.e("TUT", buttonPin + " bus cannot be closed, you may experience errors on next launch.", e);
        }
    }

}